As explained in Ref. [1]}, the effect on the matter power spectrum (MPS)
compared to a model with no interaction between the fluid and the DM, is a linear suppression in \(\log k\)  space
with a slope proportional to the momentum transfer rate,
\(\frac{P_{\text{ interacting}}}{P_{\text{not-interacting}}} & \simeq {\left\lbrace \begin{array}{ll}1 & k \ll k_{s.o.} \\1 - \sqrt{2}\, \Gamma \!/\!H\times \log k / k_{s.o.}& k \gg k_{s.o.}\end{array}\right.}~.\) 
<FIGURE>